In the last century, much of the world's energy needs have been filled by hydrocarbon fuels which provided a convenient, plentiful, and inexpensive energy source. However, as reserves of hydrocarbon fuels such as coal and oil are used, their supply becomes less certain and their cost increases. Thus, there has been intense investigation of alternative sources of energy.
Another problem of modern society, in addition to reduced resources of hydrocarbon energy supplies, is increasing waste disposal problems. In parts of the United States, suitable locations for disposing of solid waste are in short supply, requiring solid waste to be transported to distant locations. Moreover, disposal of solid waste can create pollution problems, such as contamination of ground water.
An example of where solid waste disposal is fast becoming a significant problem is the situation in Southern California. About 50,000 tons of refuse are generated daily in Los Angeles County alone. Landfill capacity close to the source of waste generation is being exhausted, and new capacity is difficult to obtain due to public opposition and regulatory constraints. These factors are exerting enormous pressure to reduce landfill use and are forcing landfills to be located near remote areas, necessitating significant transportation expense. Further, transportation of large quantities of refuse to distant locations requires energy consumption, exacerbating the problem of reduced hydrocarbon energy supplies.
There have been attempts made to reclaim and recycle solid waste, where portions of the solid waste, namely refuse-derived fuel ("RDF"), are burned to produce energy, thereby helping to solve the problem of reduced energy supplies. A significant problem with this approach is that the refuse-derived fuel, which comprises plastic and paper, is of low bulk density, typically five to ten pounds per cubic foot. Because of this low bulk density, RDF is very difficult to feed to a combustion system. To overcome this problem, the RDF is compressed and pelletized. However, the energy costs associated with compressing the RDF significantly offsets the energy gained by burning the RDF, and in some instances, can render the process uneconomical.
Accordingly, there is a need for a system for combusting refuse-derived fuel and recovering energy from the combustion, where it is not necessary to compress the RDF prior to combustion.